1. Field of the invention
This invention relates to tuners and more particularly to pushbutton tuners for radio receivers.
2. Description of the Prior Art
One of the problems of core tuning mechanisms used in pushbutton radios, specifically in pushbutton car radios, is that, because of mechanical tolerances in the construction of the tuner mechanism, the positioning of the core with respect to the coil that it tunes is not consistent as between successive operations of the same pushbutton. This inconsistency results from two types of undesirable shifts in the relative positions of cooperating components as a result of operation of the pushbuttons. Those shifts can be in the direction of the desired slug or core motion and at right angles to the desired core motion. The first shift results in the ferrite core's being inserted a lesser or greater distance than is proper for the tuning of the circuit, including the coil, to the desired frequency. The lateral inaccuracy in core or slug positioning results in mechanical binding of the core with the coil form and a change in the tuning of the circuit including that coil for a given pushbutton setting.
Methods have been devised for reducing inaccurate positioning of the core in the direction of intended motions, thereof. For example, a spring has been inserted between the core frame, or driven member, and the transfer frame, or driving member, to keep the separation of certain points on those members fixed despite relative motion of those members. However, such a method does not prevent lateral displacement of the core frame and, thus, does not assure accurate reproducibility of tuning with repeated use of the same pushbutton.